1. Field of the Invention
This invention relates to pulse width modulation for displays, more particularly for non-terminating sequences for these displays.
2. Background of the Invention
Spatial light modulator (SLM) displays utilize light transmitted or reflected by individual elements. The light transferred to the display surface form a viewable image. Digital SLMs typically receive the data for each element as a predetermined number of bits. More bits of data result in a more accurate representation of the picture element (pixel). The human eye has an analog response, so the digital data represents the analog value of any pixel. Higher numbers of bits give a better representation.
The elements transfer light for each bit of data, which the eye integrates into a given intensity. Use of 8 bits of data results in 256 gray shades. Each of the 8 bits, for example, can have the value of either a 1 or a 0. The element transfers light to the final imaging plane when the data is a 1, and does not transfer light when the data is a 0, although some systems use the reverse.
The significance of the bit determines the amount of time given to that bit to transfer or not transfer light. When the image is sampled for digitization, the information is coded into the data for each element by bit significance. The most significant bit (MSB) receives approximately half of the time allocated for that data, with each lesser significant bit receiving halves of the time allocated to its next most significant bit (i.e., values would be approximately xc2xd, xc2xc, xe2x85x9, {fraction (1/16)}, etc.). The sequence results in a series of light pulses for varying times that the eye integrates into a dot of a certain intensity.
These systems add color with the use of color filters or colored light sources. In a color-sequential system, typically only one device is used with an arrangement that changes the color of the light striking the device either with color filters or colored light sources. The same number of bits represents each color, and the eye integrates the images into a color image. Color filters can be implemented in several ways. A typical implementation uses color wheel rotating in front of the light source.
Most color wheels have three segments, red, green and blue, although variations exist. As each segment moves between the light source and the SLM, data for that color segment is used. Currently, PWM sequences, such as those described above, stand independently of previous or subsequent sequences. The device clears its data at the end of one sequence and prior to the next sequence. No light is transferred to the image plane during this clearing time. This wastes time that could be used to transfer light, which would raise the image brightness, as well as causing other problems.
Therefore, a method of addressing digital SLMs for display is needed that eliminates this independence between sequences, making the sequences seamless and allow utilization of time that would otherwise have been wasted.
One embodiment of the present invention is a method to operate a digital spatial light modulator (SLM) display using pulse-width modulation (PWM) in which the sequences of PWM are sequentially linked. The start of a new sequence of PWM terminates the previous sequence, rather than the previous sequence being terminated prior to the start of the new sequence as was done prior to this invention.
The new sequence of PWM could be the start of a different color in color-sequential systems, or the start of the next video frame.
It is an advantage of the invention in that it eliminates any off time of the device, allowing better utilization of the light, producing brighter images.
It is a further advantage of the invention in that it has flexibility to allow the use of different types of sequential color light sources.
It is a further advantage of the invention in that it allows use of other PWM related techniques.